Made JSON_USE_EXCEPTION's value in config.h a default that can be overridden.

This allows users to override it with their compiler invocation. For example:

    g++ -D JSON_USE_EXCEPTION=0 ...

Author: jacobsa

include/json/assertions.h

@@ -13,10 +13,10 @@
 # include <json/config.h>
 #endif // if !defined(JSON_IS_AMALGAMATION)
 
-#if defined(JSON_USE_EXCEPTION)
+#if JSON_USE_EXCEPTION
 #define JSON_ASSERT( condition ) assert( condition );  // @todo <= change this into an exception throw
 #define JSON_FAIL_MESSAGE( message ) throw std::runtime_error( message );
-#else  // defined(JSON_USE_EXCEPTION)
+#else  // JSON_USE_EXCEPTION
 #define JSON_ASSERT( condition ) assert( condition );
 #define JSON_FAIL_MESSAGE( message ) { std::cerr << std::endl << message << std::endl; exit(123); }
 #endif

include/json/config.h

@@ -24,9 +24,11 @@
 /// Only has effects if JSON_VALUE_USE_INTERNAL_MAP is defined.
 //#  define JSON_USE_SIMPLE_INTERNAL_ALLOCATOR 1
 
-/// If defined, indicates that Json use exception to report invalid type manipulation
-/// instead of C assert macro.
+// If non-zero, the library uses exceptions to report bad input instead of C
+// assertion macros. The default is to use exceptions.
+# ifndef JSON_USE_EXCEPTION
 # define JSON_USE_EXCEPTION 1
+# endif
 
 /// If defined, indicates that the source file is amalgated
 /// to prevent private header inclusion.